1. Field of the Invention
This invention generally relates to methods and apparatus for knee arthroplasty, including implants, guides, tools and techniques for the femur and/or tibia.
2. Related Art
Different methods and apparatus have been developed in the past to enable a surgeon to remove bony material to create specifically shaped surfaces in or on a bone for various reasons including to allow for attachment of various devices or objects to the bone. Keeping in mind that the ultimate goal of any surgical procedure is to restore the body to normal function, it is critical that the quality and orientation of the cut, as well as the quality of fixation, and the location and orientation of objects or devices attached to the bone, is sufficient to ensure proper healing of the body, as well as appropriate mechanical function of the musculoskeletal structure.
In total knee replacements, a series of planar and/or curvilinear surfaces, or “resections,” are created to allow for the attachment of prosthetic or other devices to the femur, tibia and/or patella. In the case of the femur, it is common to use the central axis of the femur, the posterior and distal femoral condyles, and/or the anterior distal femoral cortex as guides to determine the location and orientation of distal femoral resections. The location and orientation of these resections are critical in that they dictate the final location and orientation of the distal femoral implant. It is commonly thought that the location and orientation of the distal femoral implant are critical factors in the success or failure of the artificial knee joint. Additionally, with any surgical procedure, time is critical, and methods and apparatus that can save operating room time, are valuable. Past efforts have not been successful in consistently and/or properly locating and orienting distal femoral resections in a quick and efficient manner.
The use of oscillating sawblade based resection systems has been the standard in total knee replacement for over 30 years. Due to their use of this sub-optimal cutting tool, the instrumentation systems all possess certain limitations and liabilities.
Perhaps the most critical factor in the clinical success of TKA is the accuracy of the implant's placement. This can be described by the degrees of freedom associated with each implant; for the femoral component these include location and orientation that may be described as Varus-Valgus Alignment, Rotational Alignment, Flexion-Extension Alignment, A-P location, Distal Resection Depth Location, and Mediolateral Location. Conventional instrumentation very often relies on the placement of ⅛ or 3/16 inch diameter pin or drill placement in the anterior or distal faces of the femur for placement of cutting guides. In the case of posterior referencing systems, the distal resection cutting guide is positioned by drilling two long drill bits into the anterior cortex. As these long drills contact the oblique surface of the femur they very often deflect, following the path of least resistance into the bone. As the alignment guides are disconnected from these cutting guides, the drill pins will “spring” to whatever position was dictated by their deflected course thus changing their designated, desired alignment to something less predictable and/or desirable. This kind of error is further compounded by the “tolerance stacking,” inherent in the use of multiple alignment guides and cutting guides. Another error inherent in these systems further adding to mal-alignment is deflection of the oscillating sawblade during the cutting process. The use of an oscillating sawblade is very skill intensive as the blade will also follow the path of least resistance through the bone and deflect in a manner creating variations in the cut surfaces which further contribute to prosthesis mal-alignment as well as poor fit between the prosthesis and the resection surfaces. Despite the fact that the oscillating saw has been used in TKA for more than 30 years, orthopedic salespeople still report incidences where poor cuts result in significant gaps in the fit between the implant and the bone.
It is an often repeated rule of thumb for orthopedic surgeons that a “Well placed, but poorly designed implant will perform well clinically, while a poorly placed, well designed implant will perform poorly clinically.” One of the primary goals of the invention described herein is to eliminate errors of this kind to create more reproducible, consistently excellent clinical results in a manner that requires minimal manual skill on the part of the surgeon.
None of the previous efforts of others disclose all of the benefits and advantages of the present invention, nor do the previous efforts of others teach or suggest all the elements of the present invention.